The present invention relates to a heat exchanger, and more particularly, to defrosting the heat exchanger using electrical heat.
Refrigeration systems are well known and widely used in supermarkets and warehouses to refrigerate food product displayed in a product display area of a refrigerated merchandiser or display case. Conventional refrigeration systems include an evaporator, a compressor, and a condenser. The evaporator allows heat transfer between a refrigerant and a fluid passing over coils of the evaporator. The evaporator transfers heat from the fluid to the refrigerant so that the fluid cools the product display area. The refrigerant absorbs heat from the fluid in a refrigeration mode. In the refrigeration mode, the compressor mechanically compresses the evaporated refrigerant from the evaporator and feeds the superheated refrigerant to the condenser, which cools the refrigerant. From the condenser, the cooled refrigerant is fed through one or more expansion valves to reduce the temperature and pressure of the refrigerant, and then the refrigerant is directed through the evaporator.
Since most evaporators in a merchandiser operate at evaporating refrigerant temperatures that are near or lower than the freezing point of water (i.e., 32 degrees Fahrenheit), water vapor from the fluid freezes on the evaporator coils and creates frost. The frost decreases the efficiency of the heat transfer between the evaporator and the fluid (often the fluid is air in a merchandiser), which causes the temperature of the refrigerated space to increase above a desired level. Maintaining the correct temperature of the refrigerated space is important to maintain the quality of the stored food products. To do this, the evaporators must be defrosted regularly in order to reestablish efficiency and proper operation.
Some existing refrigeration systems defrost the evaporator using convection (a heating element that heats the air), which melts the frost over a period of time. This method often results in wasted heat because some of the heated fluid escapes into the product display area, potentially spoiling the food product.
Other conventional refrigeration systems include valves that direct superheated vapor from a discharge line of the compressor into the evaporator to defrost the coils (commonly referred to as “hot gas” defrost). However, the process increases energy costs necessitated by operation of the compressors that compress the superheated vapor. Other conventional refrigeration systems use a process called “reverse gas” defrost where warm refrigerant is directed through the evaporator in a direction opposite refrigerant flow during normal refrigeration mode operation. However, returning the warmed refrigerant to the system can be disruptive to normal operation of the system.